There is now only one thing I do on my initial Generation IV game and that is breeding, only because I've heard the Egg Nature trick no longer works on Platinum. (I haven't personally tried, but don't want the inconvenience XD; )
Training, I do on Platinum and it actually doesn't affect me, because I've always trained on wild Pokemon. I might only get EVs 10 at a time, (PokeRUS & Power Items) but its a method I feel more comfortable with. Not including levelling, I probably get it done in about... an hour, if I can keep my concentration from drifting. Which sometimes isn't the case... XD;;